1. Field of the Invention
The present invention relates to a motorcycle. More particularly, the present invention relates to an oil cooler located in a primary drive unit of the motorcycle and to a fan unit which can provide a cooling air flow.
2. Description of the Related Art
An air-cooled engine of a motorcycle typically has a separate oil cooler. Oil is pumped through the oil cooler, where it is cooled and then passes back to the engine. The most common form of a motorcycle oil cooler is a rectangular structure mounted to front frame members of the motorcycle. FIGS. 1-4 illustrate typical prior art oil cooler structures and their placement on a motorcycle frame. For more detail about the function and structure of a motorcycle oil cooler, reference can be had to one or more of U.S. Pat. Nos. 4,295,964; 4,662,470; 5,244,036 and 5,901,808, each of which is herein incorporated by reference.
Having an oil cooler placed on the front frame of the motorcycle is particularly advantageous in that the oil cooler resides in an air stream created by movement of the motorcycle as it travels along a road. Thus, the oil cooler can receive a cooling air flow which is used to reduce the temperature of oil passing through the oil cooler. Hence, the efficiency of the oil cooler is improved by this frontal, mostly unobstructed placement on the motorcycle.
Drawbacks have been appreciated as to having the oil cooler on the front of the motorcycle. One drawback is that the oil cooler is subject to damage from road debris (e.g. rocks, sand, bugs, trash) which can directly impact the cooling fins of the oil cooler from the roadway or get kicked up into the air by the front tire and impact the oil cooler. Such impacts can damage the oil cooler unit and lead to reduced cooling efficiency (e.g., a bent or clogged cooling fin) or engine overheating and damage (e.g., a broken or closed tube within the cooling unit).
Another appreciated drawback is that air flow through the oil cooler ceases when the motorcycle is stationary (e.g., stopped at a traffic light, stuck in traffic, slowly cruising along a beachfront street with a very slow speed limit like 5 mph). In fact, an oil cooler which produces a satisfactory drop of perhaps 20 degrees Fahrenheit in engine oil temperature when the motorcycle is traveling at road speeds, might produce an engine oil temperature drop of only 2 to 4 degrees Fahrenheit when the motorcycle is idling along in heavy traffic conditions. Such an oil temperature reduction is insufficient and can lead to engine overheating, damage and failure.
Another appreciated drawback is that the appearance of a custom motorcycle is very important to the purchaser/owner. An oil cooler typically has many complex surfaces (e.g. cooling fins or coils). Hence it is difficult to keep clean. Also because the oil cooler is very hot and sometimes splashed with water (e.g., rain), chroming on an oil cooler often becomes discolored with a blue or brown hue. Also, the oil lines to and from the oil cooler at the front of the motorcycle can be distracting to the overall appearance of the motorcycle and detract from the overall sleek appearance of the motorcycle.
Therefore, it has been desirable to hide the oil cooler on the motorcycle. One such approach to hide the oil cooler can be seen in U.S. Pat. No. 5,244,036. The solution of U.S. Pat. No. 5,244,036 is illustrated in FIG. 5, where the oil cooler is disguised as a more decorative front member, and might appeal to some riders as a spring-like structure. Further, the incoming and outgoing oil lines are moved to point very low on the motorcycle so as to not be distracting. However, the design of FIG. 5 still has drawbacks. The complex surfaces of the oil cooler are still visible and must be cleaned, the performance of the oil cooler still drops dramatically when the motorcycle stops moving, and some purchasers/owners may not desire this “springer” styling approach of hiding the oil cooler.
Another solution to hide the oil cooler can be seen in U.S. Pat. No. 6,871,628, which is herein incorporated by reference, and illustrated in FIGS. 6 and 7. In FIGS. 6 and 7, the oil cooler has been incorporated as a “snaked” pathway 60 formed within an outer cover plate 50 of an engine primary drive 14, which connects a V-twin engine 10 to a transmission 12.
Yet another solution to hide the oil cooler and to also place it in a position to receive a greater air flow can be seen in U.S. Pat. No. 6,994,150, which is herein incorporated by reference, and illustrated in FIGS. 8 and 9. In FIGS. 8 and 9, the fins 18 of the oil cooler have been integrated into the engine guard 20.
U.S. Pat. No. 6,955,150, which is herein incorporated by reference, shows a motorcycle oil cooling unit 1, as illustrated in FIGS. 10-13. The oil cooling unit 1 is mounted to down tubes 2 at the front frame of the motorcycle. An electrically operated fan 3 is controlled by an oil temperature thermostat and operates to provide a supplemental air flow to a radiator style oil cooler 4 when the oil temperature exceeds an upper threshold value.
The solution of U.S. Pat. No. 6,955,150 improves the cooling ability of the oil cooler while the motorcycle is stationary. However, the oil cooler is still distanced from the engine and attached to the front frame. Hence, extra components of the oil cooler are not well hidden or integrated on the motorcycle and electrical wires and oil lines to and from the oil cooler are also visible and distracting.